I had read about 25a just a couple of months ago in an excellent book by David Bellos, 'Is That a Fish in Your Ear?' The creator of what is represented in the grid by five letters to be removed entirely was Gilbert Adair, which multiplied my admiration of the puzzle enormously.
As some have said, the enjoyment is much enhanced by reading up on the whole fantastic exercise. Adair's version includes a 12-line rewrite of a poem by Poe (Quoth that Black Bird, "Not Again") which is worth the price of the (Bellos) book alone.
Sorry - the puzzle. Yes, I thought 21D must involve 'fish', and my only quibble was with 11D, in which 'in' seems to be doing double duty.